During embryonic development, the heart becomes innervated by sympathetic nerves, which control heart rate and contractility. Sympathetic nerve extend along blood vessels to reach their targets, in what is called neurovascular congruency, but virtually nothing is known of how these axons are instructed to reach the heart in order to establish a precise circuitry. New observations described in this proposal lead to a model in which endothelin signaling from specific vascular components is a critical guidance mechanism for sympathetic axons to take appropriate routes in order to reach the heart. In this application, using both in vivo and in vitro assays, I propose experiments to address the spatial and functional role of specific components of endothelin signaling in cardiac axon guidance. I approach this strategy within a developmental context that coordinates neuronal outgrowth with cardiovascular cell lineage and morphogenesis.